<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button"value="加" onclick="f()">
<input type="button"value="减" onclick="f1()">
<input type="button"value="乘" onclick="f2()">
<input type="button"value="除" onclick="f3()">
<div>结果</div>
<script>

    let i1= document.querySelector("#i1");
    let i2= document.querySelector("#i2");
    let d=document.querySelector("div");

    function f() {
        if (isNaN(i1.value)||isNaN(i2.value)){
            d.innerText = "输入错误!";
            return;
        }
        d.innerText = "结果:"+ (i1.value*1+i2.value*1);
    }
    function f1() {
        if (isNaN(i1.value)||isNaN(i2.value)){
            d.innerText = "输入错误!";
            return;
        }
        d.innerText = "结果:"+ (i1.value-i2.value);
    }
    function f2() {
        if (isNaN(i1.value)||isNaN(i2.value)){
            d.innerText = "输入错误!";
            return;
        }
        d.innerText = "结果:"+ (i1.value*i2.value);
    }
    function f3() {
        if (isNaN(i1.value)||isNaN(i2.value)){
            d.innerText = "输入错误!";
            return;
        }
        d.innerText = "结果:"+ (i1.value/i2.value);
    }

</script>
</body>
</html>